The progress with E31 was slower than I wanted. I was sick, parts got lost in the mail - nevertheless, the progress has been made!

To pick up where I left off - got new belts, pulleys, one tensioner was stuck so I got a replacement one and also put radiator cleaner in the coolant to flush the gunk out. Since then, I flushed the cooling system 4 times until the water started coming out fairly clean.

The pulleys are actually NSK which are an official bearing supplier for Bosch, great quality.

Added 1 bottle of Liqui Moly engine cleaner and then replaced oil and filter after. Even with this cleaner, the oil that came out was actually clean.

Worlds filthiest cabin filters from 1990.

Found a fuel leak at the back of the engine which was sorted easily.

Then I pulled and checked all of the fuses and reseated all relays just because the car has been standing for a while.

The main issue with the car was that it would start up, idle crappy and once it starts to warm up, it would grossly misfire and choke when I give it gas.
Once I turn it off, it wouldn't stay running again, it only starts for a second or two and then stalls.

Clearly a big issue. I wanted to pull codes and it took me 3 weeks to get INPA to work on E31 and I ended up buying an old Dell D620 laptop with a serial port cause that was the only way to make it work.

After much trial and error, I successfully set up INPA and managed to pull some codes and live data. In the meantime, I also used Foxell NT510 which was surprisingly able to talk to DME, EKM and ZKE modules of the car.

Didn't get any useful codes and DME was mainly code free. I did get one code for the fuel tank breather valves aka purge valves.

Upon closer look, I found that some genius butchered the fuel breather system by splicing some wires, chopping off factory connectors and making vacuum lines out of electrical tape.

Didn't know if I should cry or laugh when I noticed this.

The paint a better picture, the fuel breathing system on E31 works like this - vacuum line goes from the fuel tank to the valve under the rear right fender, then a line to the carbon canister in the engine bay and from the canister to the Y piece connector which splits it to two purge valves which are feeding each throttle body on bank 1 and 2.

What morons did: remove one purge valve entirely, cut off both factory connectors (why wouldn't you?) and split the lines after the valve and feed throttle bodies with just one valve and top it all off with making vacuum lines out of electrical tape.

I've seen some butchery done on cars before but this takes the medal.

Luckily, I was able to trace back the original wires in the loom and re-did everything back to stock with new wires and proper connectors.

Two wires that were cut and sticking out of the loom turned out to be leftovers of the original wires which they were too lazy to remove.

These are just typical Bosch EV1 connectors.

I bought one new valve and tested the old one, I measured the resistance with a multimeter which was good at 44 kOhm, applied 12V on it and made sure it holds pressure with a hand vacuum pump. The original Y connector is made of plastic and NLA so I got a better one made of brass.

Everything assembled.

Next, I focused on ignition wires which were original and considering age due for replacement. One of the common issues for this engine to start and stall after a couple of seconds are cylinder identification sensors aka donuts. These sensors are mounted on wires #6 & #12, if the signal is absent the engine will run for 2 seconds and then the injectors will be inhibited to prevent wash-down of the cylinders. Courtesy info from Timm from the UK.

There are 2 options when it comes to new wires. Either get a whole set with new sensors already installed on the wires and pay around $450 or cheaper route of getting just the wires and new sensors separately and installing them myself. Guess which one I took

Installing new donut sensors was a bit tricky but once I got the hang of it, it was easy. A plug on the wire needs to be removed and the sensor just slides on the wire.

Then I verified proper installation with a multimeter and the wires were ready to be installed.

Out with the old wires.

New wires neatly labeled and repacked in the original brackets which were without any damage and in good condition.

Earlier I measured the resistance on the crank position sensors - 488 kOhm which is kinda on the limit (repair manual says 540 kOhm +/- 10%) so I got a pair of new sensors and replaced them.

These sensors are located at the front of the engine. I had to unbolt the PS pump to get enough room to remove/install the sensor. I beat up my hands pretty good when doing this job.

Borrowed a pic from the internet to show location.

And pièce de résistance - new plug caps for the vent holes on the throttle bodies. The old ones were cracked and perished. Cheapest part I bought so far at ~ 2 bucks a piece.

After all of this, the car was still running like a turd - no change. Misfiring and barely stay running when warmed up.

Then I turned to test the fuel pressure which I had plans to do a while back just didn't get around it. I bought a cheap fuel pressure gauge which turned out the be total crap and leaked all over when I attached it on the lines at the back of the engine, but even with it leaking there was hardly any pressure, less than 1 bar when the car was running for a brief moment.

That was no bueno and I decided to pull the fuel pump assembly out. Fortunately, I bought new pumps some time ago because I was planning to replace them preveniently.

With the pumps out, I found that both rubber lines that go from the pumps had sizeable cracks in them.

Combine that with old weak pumps and they simply didn't supply proper fuel pressure. No wonder the car was running like a turd.

The strainer was crispy and falling apart.

The bracket that's holding fuel pumps removed.

Original Bosch pumps.

New Polish pumps worked a treat. Very happy with the quality and the design was identical to Bosch pumps.

Everything reassembled and ready to go back in the fuel tank.

I read somewhere that the new gasket for the fuel tank is a must so I got one.

I think the most annoying part of this job was replacing these 2 short fuel lines going from the pump to the metal pipe connection in the underbody, but I had to replace them since they were rock hard and they would leak for sure. Also, lining up the fuel pump assembly with the new gasket was a pain. I counted 2 and 1/4 turns when removing the plastic lock ring so I went with the same when putting it back.

Fired up the old girl and lo and behold a different car! It started after just a couple of seconds while before it used to crank and crank.

Inspired by this, I took her for the maiden voyage out of the garage on the next day.

She is working beautifully! Engine sounds sweet and idles great, cold start is also good. There was a lot of condensation and I let the car work for 30-40 minutes and eventually it all cleared up and exhaust was smoke-free!

I drove it up and down the courtyard and clutch is great, I got it up to 3rd speed and it slots in all gears perfectly and without any slop. Even the power steering pump is working noise free after exchanging around 5L of correct fluid!

Here's a little video. Injectors are clicking loudly since the sound insulation is removed.

So far so good. This car was a roller coaster with ups and downs, it took a lot of effort but I'm very excited for bringing back to life this neglected icon.

There's more mechanical stuff to be done, but next I wanna see that interior clean up which will have to wait for a bit better waether.

I've done some stuff on the M5 as well which I'll post in the upcoming days. At the moment screws on the alternator housing are stopping me from replacing the noisy bearings.

Dude. I’m in awe of your ability to not only fix the issues you fix, but to seemingly do so with such calm and logic. If I found that hack job you just resolved I probably would’ve gone inside, defeated, and consumed a large quantity of beer. Meanwhile I’m still driving around without an ambient temp sensor because the carport is too cold and damp for my sensitive bitch-self to crawl under one corner of the car for 15 minutes and splice the wires back together.